This invention finds use in a number of microwave circuit applications which require full 360 degree linear phase control of a carrier signal. Examples of such applications include continuous phase modulation (CPM) and indirect frequency modulation (FM) radio communication transmitters, phase synchronisation of antenna and oscillator arrays, and phased array antenna beam steering.
Most microwave linear phase shifters are based on a single stage reflection topology using a circulator or coupler with appropriate reflective terminations. Large range phase shifters at these frequencies have been designed with some success as a cascade of smaller range single stage shifters. Another method of obtaining large range linear phase shift at microwave frequency is by detuning the tank circuit of an injection locked oscillator.
The problem with these traditional implementation strategies is that the circuitry required to implement the full 360 degree phase shift range becomes quite complicated. At microwave frequencies, this complicated circuitry can become quite inhibitive and can reduce the performance significantly on implementation. Also, phase shift linearity has to be sacrificed in order to maintain acceptable bandwidth. As a result of poor phase shift linearity over the full 360 degree range, complicated predistortion circuitry is required on the phase control signal to realize acceptable phase shift linearity.